Aided by Zembabwean Wyvern-riders and black Amazons, King Conan of Aquilonia and his son Prince Conn track their arch-foe, Stygian sorcerer Thoth-Amon, to the extreme southern end of the Hyborian continent.
The sorcerer has taken refuge with the last remnants of the evil Serpent Men, shape-changers who have menaced mankind throughout its prehistory. Conan's host locates their skull-cave redoubt, only to fall victim to their ploy of emulating beautiful Stygian women.
His final battle with Thoth-Amon in the sorcerer's own domain proves as hard-fought as their previous encounters, but is ultimately successful at ridding the world of the fiend. It is in fact Conan's 13-years old son Conn who deals the death blow to his father's old arch-enemy.